Conventionally, a vacuum chamber has been manufactured by machining a material block into a chamber or connecting plates by using welding or soldering, in view of ensuring a durability and an airtightness against an atmospheric pressure. However, in the case of performing a cutting process by using a machine, since a lot of material should be cut, it takes a long time for processing and a large amount of the material wastes. Further, in the method of welding or soldering, deformations caused by applied heat should be removed or a finishing processing should be performed therefor, which increases a manufacturing cost thereof.
Recently, as target substrates are scaled up, the size of a processing chamber is also increased. For example, in the manufacturing process of FPD, a large-sized glass substrate, having a rectangular shape whose long side is more than 2 m, is received in the processing chamber and the processes such as etching, ashing and film formation are performed in a vacuum state. Further, in a vacuum chamber for processing such a large-sized glass substrate in a vacuum state, a metallic chamber made of aluminum or the like is required to have a sufficient stiffness to withstand the atmospheric pressure with the inside thereof kept in a vacuum state.
Accordingly, in the integrated vacuum chamber manufactured by the conventional machining or welding, walls of the chamber should be thick sufficiently, which increases the weight thereof. Further, a large machine is needed to machine it, so that a manufacturing cost is increased. Further, if the vacuum chamber is scaled up to exceed a certain size, a legal restriction is imposed on its transportation, so that a transportation cost is increased.
As a technology of manufacturing a vacuum chamber by other method than the machining and the welding, there has been provided a vacuum chamber which uses a plurality of plates tightly joined in a box-shape by structure bolts; seal members continuously provided, along the joint lines of the adjacent plates, at the inner side thereof; and press members attached by fastening bolts, each press member pressing the seal member against the joint line to airtightly seal the joint line (see, e.g., Japanese Patent Laid-open Application No. H9-209150 (FIG. 4): Reference Document)
Since the vacuum chamber of the Reference Document includes the plates and the seal members, it is possible to assemble them at an installation place and there is a little restriction to transportation thereof. Further, the vacuum chamber can be made at a lower cost compared with the case of manufacturing a vacuum chamber by using the conventional machining or welding. However, in the vacuum chamber having a structure constructed by combining and joining plates as described in the Reference Document, it is difficult to ensure an airtightness at the corner of the chamber.
In the Reference Document, for example, a branched seal member is used where three plates are joined at the corner, wherein branches of the seal member are extended at a right angle with respect to each other in three-directions along joint lines of the plates. However, a three-dimensional mold is required to manufacture such a branched seal member, so that cost increase is inevitable.
Further, in the seal mechanism disclosed in the Reference Document, a sealing is obtained by pressing an elastomer against the joint lines of the plates with a specific force. However, it is difficult to sufficiently press the branched seal member at the corner of the vacuum chamber formed by three plates, and it may be impossible to maintain the inside of the vacuum chamber in a vacuum state.